Band-Pass Filter for Stable Single-Mode Lasing in Optical Devices

An optical band-pass filter is introduced as an intermediary element between the gain medium and the GMR tunable mirror. This filter transmits only the desired DWDM channels range (C-band or L-band) while blocking wavelengths outside this range, thereby preventing spurious reflections and secondary peaks from causing multimode oscillation. The filter acts as a mediator that allows the GMR mirror to provide broad tuning capability while ensuring stable single-mode lasing within the specified channels range.

The patent converts the potentially harmful effect of the gain medium's wide effective gain range into a benefit by using it to provide sufficient gain across the DWDM channels range, while the optical band-pass filter eliminates the harmful spurious reflections and secondary peaks outside this range. The wide gain range ensures adequate amplification for all desired channels, and the filter selectively allows only the beneficial wavelengths to oscillate, transforming the broad gain spectrum from a source of unwanted modes into an advantage for comprehensive channel coverage.

Instead of modifying the GMR mirror design to eliminate secondary reflection peaks, the patent extracts and removes these unwanted wavelengths from the optical path using an optical band-pass filter. This approach allows the GMR mirror to maintain its simple, efficient structure with broad tuning capability, while the filter selectively removes the harmful secondary peaks and spurious reflections outside the DWDM channels range, achieving single-mode operation without complicating the mirror's fabrication.